The present invention relates to fiber-optic cable used for the conducting optical signals. More particularly, the present invention relates to a guide boot for bending a fiber-optic cable, and maintaining the bend radius of the fiber-optic cable at or above a predetermined value.
Fiber-optic cables are commonly used to transmit optical signals between optoelectronic devices. A conventional fiber-optic cable can include an optically-conductive optical fiber, and a protective inner jacket that surrounds the optical fiber and protects the optical fiber from buckling. The inner jacket can be surrounded by a layer of protective fibers having sufficient strength to withstand the maximum anticipated tensile forces on the fiber-optic cable. The protective fibers can be enclosed in a flexible outer jacket.
Excessive bending or twisting of a fiber-optic cable can degrade the quality of the optical signals transmitted through the fiber-optic cable. In extreme cases, excessive bending or twisting can break the optical fiber within the fiber-optic cable. In practice, fiber-optic cables must often be bent to facilitate routing to, from, or within equipment such as computers, connector panels, junction boxes, etc. Accordingly, fiber-optic cables are typically evaluated to determine a minimum bend radius. The minimum bend radius represents the minimum radius at which the fiber-optic can be bent without potentially degrading signal-transmission quality, or damaging the optical fiber within the fiber-optic cable.
Connectors are commonly used to couple fiber-optic cables to other fiber-optic cables, or to optoelectronic devices such as sources, detectors, repeaters, switches, attenuators, etc. The point at which a fiber-optic cable enters a connector is particularly susceptible to being bent in excess of, i.e., more sharply than, the minimum bend radius for the fiber-optic cable.
A guide boot is often used to maintain the bend radius of a fiber-optic cable at or above the minimum bend radius as the fiber-optic cable approaches and enters a connector. FIGS. 1A and 1B depict a conventional guide boot 100 used in conjunction with an LC-type connector 102 and a fiber-optic cable 104. The figures are each referenced to a common coordinate system 11 depicted therein.
The cable 104 is mechanically coupled to the connector 102 using a metallic crimp sleeve 106 and a shrink tube 108 (see FIG. 1B). The crimp sleeve 106 is crimped over a substantially cylindrical rear mating portion 102a of the connector 102. The shrink tube 108 securely grasps the crimp sleeve 106 and the outer jacket of the cable 104, and thereby secures the cable 104 to the crimp sleeve 106 (and the connector 102).
The guide boot 100 has passages formed therein for receiving the cable 104. The guide boot 100 is mated with the connector 102 by threading a free end of the cable 104 through the passages, and advancing the guide boot 100 along the cable 104.
A forward, or mating, portion 112 of the guide boot 100 eventually reaches the crimp sleeve 106 as the guide boot 100 is advanced along the cable 104, as shown in FIG. 1B. A force (hereinafter referred to as an xe2x80x9cinsertion forcexe2x80x9d) is exerted on the guide boot 100 to advance the mating portion 112 over the crimp sleeve 106 (and over the portion of the shrink tube 108 installed over the crimp sleeve 106), in the direction denoted by the arrow 120 in FIG. 1B.
The crimp sleeve 106 becomes disposed within the passage in the mating portion 112 as the guide boot 100 is advanced over the crimp sleeve 106. The insertion force needed to advance the guide boot 100 is due, in part, to friction between an inner surface 116 of the mating portion 112, and the portion of the shrink tube 108 installed over the crimp sleeve 106. The guide boot 100 is retained on the connector 102 primarily by friction between the inner surface 116 of the mating portion 112 and the crimp sleeve 106.
The guide boot 100 includes a curved body portion 116. The body portion 116 should have a radius of curvature approximately equal to or greater than the minimum bend radius of the cable 104. The body portion 116 imparts a corresponding curve to the cable 100 when the cable 100 is installed the passage 110. The body portion 116 is sufficiently rigid to prevent the cable 104 from being bent in excess of its minimum bend radius.
The guide boot 100 can be rotated in relation to the connector 102 to direct the cable 104 toward a desired location. The guide boot 100 is rotated by imparting a torque to the guide boot 100 sufficient to overcome the friction between the inner surface 116 of the mating portion 112 and the crimp sleeve 106. (The cable 104, which is secured to the connector 102 by way of the shrink tube 108 and the crimp sleeve 106, normally rotates with the mating portion 112, and in a perfect world would do so without any twist being imparted thereon.)
However, the insertion force needed to advance the guide boot 100 over the shrink tube 108 until it reaches the crimp sleeve 106 in many instances damages the shrink tube 108. Such is shown in FIGS. 1C and 1D. In particular, the force needed to overcome the friction between the inner surface 116 of the mating portion 112 and the portion of the outer surface of the shrink tube 108 installed over the crimp sleeve 106 will deform, tear, or otherwise damage the shrink tube 108.
This damage to the shrink tube 108 can cause the shrink tube 108 to lose its firm grasp of the rear mating portion 102a of the connector 102. Furthermore, damage to the shrink tube 108 will result in a loss of the frictional/interference fit between the shrink tube 108 and inner surface 116. Thus, rotating the guide boot 100 to a desired orientation on the connector 102 when the shrink tube 108 has been damaged and its grasp on the rear mating portion 102a of the connector 102 lost, can cause a corresponding rotation of the cable 104. Rotating the cable 104 in this manner will twist the underlying optical fiber, which is independently restrained from rotation within the connector 102. Twisting the optical fiber can degrade the light-conducting characteristics thereof, and can thereby decrease the quality of the signals transmitted through the cable 104. Moreover, twisting of the optical fiber, if extreme, can break the optical fiber.
A preferred embodiment of a guide boot for a fiber-optic cable mechanically coupled to a connector comprises a mating portion having an interior surface defining a passage for receiving a portion of the connector and the fiber-optic cable, and a plurality of ribs formed on the interior surface and extending along at least a portion of a length of the mating portion. A preferred embodiment also comprises a body portion adjoining the mating portion and having an interior surface that defines a passage for receiving the fiber-optic cable. The interior surface of the body portion is curved so that the body portion bends the fiber-optic cable.
A preferred embodiment of a guide boot for bending a fiber-optic cable mechanically coupled to a connector by way of a crimp sleeve and a shrink tube comprises a mating portion. The mating portion has an interior surface defining a passage for receiving the crimp sleeve and a portion of the shrink tube installed over the crimp sleeve. The passage has a diameter greater than an outer diameter of the portion of the shrink tube installed over the crimp sleeve and the interior surface has a plurality of ribs formed thereon for contacting the crimp sleeve. A preferred embodiment also comprises a body portion adjoining the mating portion and having an interior surface defining a passage for receiving the fiber-optic cable.
A preferred embodiment of a system for conducting optical signals comprises a connector, a crimp sleeve fixed to the connector, a fiber-optic cable, and a shrink tube having a first portion fixed to the crimp sleeve and a second portion fixed to the fiber-optic cable. A preferred embodiment also comprises a guide boot comprising a mating portion. The mating portion has an interior surface defining a passage for receiving the crimp sleeve and the first portion of the shrink tube. The passage has a diameter greater than an outer diameter of the first portion of the shrink tube and the interior surface has a plurality of ribs formed thereon for contacting the crimp sleeve. The mating portion also comprises a body portion adjoining the mating portion and having an interior surface defining a passage for receiving the fiber-optic cable.
A preferred method for mating a guide boot with a connector mechanically coupled to a fiber-optic cable by way of a crimp sleeve and a shrink tube comprises inserting the fiber-optic cable through a passage formed in the guide boot, advancing the guide boot along the fiber-optic cable, advancing the guide boot onto the crimp sleeve so that a plurality of ribs formed on an internal surface of the guide boot interferely contact the crimp sleeve and a portion of the shrink tube installed over the crimp sleeve, and rotating the shrink tube so that the fiber-optic cable extends from the guide boot in a desired direction.